Hand-held tester and method for local area network cabling

ABSTRACT

A LAN tester has display and remote units each having a connector jack attached to an adapter board for connection to the plug of a patch cord. Both the display and remote units have circuits which are capable of measuring the phase between a drive signal voltage and the corresponding coupled or reflected signal due to the drive signal. Scattering parameters for the mated connector pairs and the patch cord itself are measured during a field calibration. A computer in one or both of the tester units stores the measured scattering parameters and uses the scattering parameters to move the reference plane to any desired location along the patch cord. Channel link or permanent link tests can be conducted using the same equipment.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of co-pending application Ser. No.10/317,555 filed Dec. 12, 2002.

BACKGROUND OF THE INVENTION

Local area network (LAN) cabling is used to connect equipment such aspersonal computers, printers and fax machines that pass informationbetween them using high-speed digital signals. This type of highperformance cabling is sometimes referred to as telecommunicationscable. Since an office contains many computers, computer file servers,printers, and fax machines, the LAN cabling interconnects all of thisequipment into a communications network. LAN cabling has been designedto support telecommunication between all of the individual elements ofthe network.

FIG. 1 shows an example of LAN cabling, in a simplified drawing. FIG. 1shows how the LAN cabling, most of which runs within the building walls,is used to connect the personal computer 1 at someone's desk to the fileserver 2 in the telecommunications room. The maximum length of cable 3inside the wall cannot exceed 90 meters. Wall jack connectors 4 are usedto connect the cords 5 from the computer and file server to the LANcabling.

Cabling: Cabling is an important word in the term LAN cabling becausecabling includes the connectors 4 placed on the LAN cable as well as thecable 3 itself. Thus, the performance of the LAN cabling depends uponthe connectors as well as the cable.

Installation: Technicians install the LAN cabling as a part of newconstruction or as part of a LAN performance upgrade in existingstructures. In either case, the technicians pull the LAN cable 3 throughthe walls and then place the connecting jacks 4 on the ends of thecable. The jacks are then snapped into the wall jack mounting plate andthe installation is complete.

However, the technician is then required to test each LAN cabling run orlink with calibrated test equipment. This testing certifies to thegeneral contractor that the cabling run has been correctly installedfrom the standpoint of signal integrity. Hand-held LAN testers are usedto perform these tests. The testers drive the cabling with a series ofdifferent signal types and from measurements of the received signals,determine if the cabling is capable of supporting the telecommunicationsignals at the prescribed data rate.

The LAN testers record the results of each test and, at a later time,print out a test document indicating that the link passed or failed. Thetechnician gets paid for the links that pass. If there are links thatfail, the technician must re-test, and often replace connectors thathave been incorrectly or improperly installed. The technicians keeptesting and repairing the links until they all pass.

LAN Testers: LAN testers are fairly sophisticated hand-held testsystems, which can test LAN links with a series of tests covering afrequency range of 1 to 250 MHz, in the case of TIA Category 6 cabling.FIG. 2 shows a typical LAN tester 6, with a test adapter circuit board 7connected to the LAN tester. The test adapter circuit board includes atest jack connector 8. The purpose of this test adapter is to provide aconnection interface between the LAN tester and the LAN link to betested.

The test jack 8 allows the LAN tester 6 to connect to the LAN link witha patch cord 9, as shown in FIGS. 3 and 4. Typical lengths for patchcords are two meters, or approximately six feet. This length allows thetechnician to conveniently connect the LAN tester to the wall jacks 4during test runs.

Standards: Technicians test their installed links with reference totelecommunication industry standards. In the United States the standardis specified by the TIA or Telecommunications Industry Association. InEurope the standard comes from ISO, or International StandardsOrganization. When testing a link, the technician selects which type oflink is being tested and the corresponding sets of measurement limits,whether from TIA or ISO.

The link is tested and the measured results are compared to limits fromthe specified standard. If no limits are exceeded, the link passes. Ifnot, then the link fails and the technician must work on the failedlink, as required, until it passes. Often this means reinstalling theconnectors on the ends of the cable.

Standard Link Definitions: FIG. 5 shows the standard permanent link, insimplified form, with 90 meters of LAN cable, running within astructure's wall, or overhead in the ceiling. The wall jacks, attachedto the cabling ends, are used to connect the link with equipment in thetelecommunications room and to individual items such as computers orprinters within the office's local area network. The TIA and ISO specifythe length of 90 meters as the maximum length for the permanent link.

Link Testing: FIG. 6 illustrates how the LAN testers check theperformance of a link. When testing a link (a procedure known in theindustry as “shooting” a link), two LAN testers are required as shown.The technician connects a display end LAN tester 6A at one end of thelink, and the remote end LAN tester 6B at the other end of the link.Since the display end LAN tester has a display screen to show themeasurement test results, the technician shoots the link from thedisplay end, controlling the test from there, and viewing the testresults.

During the test, first one unit applies test signals to one end of thelink while both units measure the results. Then the roles are reversedwith the signal application and signal measurement taking place at theopposite ends of the link. When the test is complete, the remote unitsends its data measurement files to the display unit for finalprocessing and storage within the display unit. The limits for eachtest, specified by the selected standard, are applied to the measurementdata set to determine if the link passed or failed the certificationtest.

Standard Links: Both the TIA and ISO have defined two types of LANlinks, the channel link and the permanent link. Each link is shown anddiscussed below.

Channel Link: The channel link includes the LAN link and the patchcords, as shown in FIG. 7, but does not include the connection to thechannel test adapter boards 7A. The channel link measurement pathincludes the link 3 inside the walls, the mated connector pairs at thewalls and the patch cords and is supposed to represent the performanceof the final, complete telecommunications link, which also uses patchcords to connect the personal computers and file servers to each other.Since there is a longer length of cabling in this path, the test limitsfor the channel link are not as stringent as those for the permanentlink.

Permanent Link: The permanent link includes the link 3, plus the matedconnector pairs at the wall jack, but it does not include the patchcord, as shown in FIG. 8. Nor does it include the connection to thepermanent link test adapter board 7B. The permanent link test evaluatesonly the cable within the walls, the connector jacks at the wall, theplugs that are inserted into the jacks, and two centimeters of cablethat is attached to each of the plugs. The permanent link testessentially represents the performance of just the link cabling withinthe walls. Consequently, the permanent link test limits are the tightestmeasurement limits to pass.

As a result, technicians are often told that if their link fails thepermanent link test, to change over the LAN tester limits to channellink limits and re-test. If the channel test passes, the link may thenbe considered to pass under these conditions.

Consideration will now be given to the test issues faced by thetechnicians as they test their installed Local Area Network (LAN)cabling for compliance with the appropriate TIA or ISO measurement testlimits. The technician will certify the installed link to eitherpermanent or channel link measurement limits. It is assumed that thetechnician has performed steps necessary to calibrate the test equipmentin the field before the LAN certification test to assure maximum LANtester measurement accuracy.

Permanent Link Testing Issues

1. Permanent Link Adapter Construction: Note the prior art permanentlink test adapters 7B shown in FIG. 8. Keep in mind the permanent linkcomprises the cable in the wall plus the mated connector pair at thewall jacks, but it does not include most of the patch cord. Thepermanent link adapters (PLA's) are typically fabricated by cutting apatch cord in half, and then soldering each of the cut patch cord endsto a printed circuit board (PCB) within the permanent link test adapterhousing. These PCB's are designed to cause very little signal integrityproblems so that their effects are ignored.

2. Permanent Link Testing Lifetime: Permanent link adapters have alimited test lifetime due to mechanical flexing of the patch cord as itenters the PLA housing. When the patch cord has been flexed beyond itsmaximum number of flexures, it will require replacement. When thishappens, the entire PLA has to be replaced. In addition, for maximumtest accuracy, both PLA's, the one at the display end and the one at theremote end should be replaced.

3. Dedicated PLA: The LAN testers often use a dedicated PLA for eachpermanent link tested. This is because the circuit and transmission lineproperties of the patch cord can be an important part of the overall PLAmeasurement result. The installation technician needs to be aware ofwhat link he or she is testing, who made the cabling, and what is thepreferred type of PLA to use.

4. Matched PLA Sets: Usually the technician will use a set of PLA'smatched to the cable type, by vendor, which is used in the link. If thelink is made with cabling, (that is, cable plus connectors), from VendorX, then a PLA made from Vendor X patch cords will be used for thecertification test.

5. PLA Cost: The PLA's can be a costly item for the installers, often$400 or more for a set of two. If the LAN cabling installation testingcompany has several installers, each requiring several different sets ofvendor specific PLA's, this overhead item can be rather costly. The costcomes from a dedicated printed circuit board, within a plastic housing,to form the structure of the PLA, which connects to the LAN tester.

6. PLA Cross-talk: In addition, as LAN certification moves tofrequencies above 250 MHz, the performance of the PLA's as a part of themeasurement system becomes more critical. The measured cross talk orlack of isolation between conductor pairs within the PLA connectioncircuit board becomes a serious issue as frequencies increase. When theisolation degrades beyond a certain level, the LAN tester cannot measurethe cabling pair-to-pair isolation because it cannot “see” past its ownPLA generated crosstalk.

The present invention provides the solution to this problem. Thesolution is to use a connector with proven isolation properties on thetest adapter board, and then to connect to that test adapter board witha patch cord having a connector which mates to the connector on theadapter board.

7. PLA Reference Plane Calibration: The last issue with permanent linkadapters is that of the measurement reference plane location. Thepurpose of permanent link calibration is to refer all permanent linkmeasurements to a known point along the patch cord. In particular, thepermanent link measurement reference plane is calculated to set thispoint at the end of the patch cord, 2 centimeters from the wall jack.From this calibration, all effects from the patch cord are removed fromthe permanent link measurement. The calibration procedure used to defineand set this reference plane at this point can involve taking an initialset of permanent link calibration data and finally referring it to thisdesired reference plane.

Channel Link Testing Issues

1. Channel Link Adapters: Note the channel link test adapters 7A shownin FIG. 7. Keep in mind the channel link includes the link (i.e., thecable in the wall plus the mated connector pairs at the wall jacks) andthe patch cords but it does not include either the plugs or the jacks atthe channel test adapter boards. The channel link adapters (CLA's) arefabricated by placing a right-angle connector with appropriate isolationon the printed circuit board mounted within the CLA housing. The rightangle connector is selected to provide significant pair-to-pairisolation when mated with the patch cord used for the channel linkcertification.

2. CLA Testing Lifetime: Channel link adapters have a much longer testlifetime when compared to permanent link test adapters since the use oflow cost replaceable patch cords solves the patch cord mechanicalflexure problem. The connector mounted on the printed circuit boardinside the CLA eventually wears out as the cladding on the contactswears off. Nevertheless, the testing lifetime for the channel linkadapter is considerably longer than that for the permanent link adapter.

3. Dedicated CLA: The LAN testers also use a dedicated CLA when testingchannel links since low cross talk, high isolation connectors 8 are usedon the channel link adapter printed circuit board.

4. Matched CLA Sets: Matched CLA sets are used by definition by virtueof the high isolation right angle printed circuit board connectorsmounted on the PCB within the CLA housing. However, when compared to thePLA, any type of patch cord can be used with the CLA, so long as thepatch cord is compliant with the cabling category used for the linkunder test.

5. CLA Cost: The CLA's are less costly than PLA's, since they can useany compliant patch cord to connect to and test the channel link.

6. CLA Cross-talk: The channel link pair-to-pair isolation is superiorto that of the permanent link by virtue of the low crosstalk connectorused within the CLA module housing.

7. CLA Reference Plane Calibration: The last issue with channel linkadapters is also that of the measurement reference plane location. Inparticular, the channel link measurement reference plane is set at theend of the patch cord connector right at the input end of the patchcord, as shown in FIG. 7. With this calibration, all effects from thepatch cord input connector (i.e., the plug at the tester end) areremoved from the channel link measurement.

LAN Link Measurement Issue Summary

From the preceding discussion, when compared to channel link adapters,permanent link measurements require the use of a separate set ofpermanent link adapters, which add an undesirable set of costs in termsof: 1) the permanent link adapters themselves; 2) the number ofdedicated PLA sets; and 3) limited PLA test lifetime due to patch cordflexure failure. Permanent link adapters also have more problems withminimizing pair-to-pair crosstalk when compared to channel linkadapters.

SUMMARY OF THE INVENTION

For these reasons, in the present invention a calibration/measurementmethod is proposed the objectives of which are to:

-   -   1. eliminate completely the permanent link test adapter;    -   2. reduce LAN measurement overhead support costs;    -   3. improve signal integrity;    -   4. increase LAN link measurement accuracy at frequencies above        300 MHz, and    -   5. provide a means to measure permanent links using channel        adapters and low cost patch cords.        Phase

Preparatory to a description of the method of the present invention, adiscussion of phase needs to be presented. The capability of phasemeasurement is a key attribute of the LAN tester of the presentinvention. That is, in addition to magnitude, the handheld LAN tester ofthis invention can measure phase. This capability permits the tester toset a measurement reference plane at one specified point along the LANlink to be measured. The original calibration reference plane may be setat a point along the link at a point, which is easy to set, measure,define and implement.

Phase also allows the tester to easily move this original calibrationreference plane and all of its associated LAN link measurements toanother, new, reference plane location at any time during the LAN linktesting. Specifically, with phase information, a display end and remoteend can each move the phase reference plane from within the channel linkadapter printed circuit board, through the mated pair of connectors atthe CLA output and anywhere down the length of the patch cord, and up tothe mated pair of connectors at the wall jack, in any of the fourpossible locations as shown in FIG. 9. Movement of the phase referenceplane enables the tester of this invention to use a channel link adapterand low cost patch cord to perform permanent link measurements.

In brief, the method involves the calibration step of measuring theoverall scattering parameters S_(T) for each of the patch cords plusmated connectors pairs at each end of the patch cords, as indicated inFIG. 10. The scattering parameters S_(B) of each patch cord can beobtained from known characteristics of the cord. This, together with thetotal scattering parameter matrix S_(T) allows calculation of thescattering parameters S_(A) and S_(C) of the mated connector pairs atthe ends of the cords. With the scattering matrices of the matedconnector pairs S_(A) and S_(C) and the patch cord S_(B) known, thereference plane may be moved anywhere along the cord from within the LANtester to perform either permanent link or channel link tests.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic sketch of a LAN cabling connection from a workarea to a telecommunications room.

FIG. 2 is a diagram of a prior art LAN tester with a test adapter andtest jack.

FIGS. 3 and 4 illustrate a prior art LAN tester connection with a patchcord.

FIG. 5 illustrates a standard 90 meter link.

FIG. 6 illustrates the process for testing or “shooting” a link with LANtesters.

FIG. 7 illustrates a channel link configuration.

FIG. 8 illustrates a permanent link configuration.

FIG. 9 illustrates movement of the measurement reference plane withphase, as taught by the present invention.

FIG. 10 illustrates the LAN testers of the present invention.

FIG. 11 is a plot of drive signal and a resulting signal measured by theLAN tester of the present invention.

FIG. 12 is an schematic diagram of the phase measurement circuit in adisplay unit of the present invention.

FIG. 13 is an illustration of setting the measurement reference planeduring factory calibration, according to the present invention.

FIG. 14 is an illustration of movement of the reference plane through amated connector pair.

FIG. 15 is an illustration of movement of the reference plane down thepatch cord, according to the present invention.

FIG. 16 illustrates how the reference plane at point 2 of FIG. 9 relatesto the reference plane at point 3 of FIG. 9.

FIG. 17 is an exploded perspective view of the LAN tester display unitof the present invention.

FIG. 18 is an exploded perspective view of the underside of the testerunit.

FIG. 19 is a block diagram of the digital control circuit board of a LANtester unit of the present invention.

FIG. 20 is a block diagram of the analog circuit board of the presentinvention.

FIG. 21 is a detailed phase measurement block diagram of the presentinvention.

FIG. 22 is a diagram of a total link and its equivalent cascade oflinear, two-port networks.

DETAILED DESCRIPTION OF THE INVENTION

A schematic representation of the LAN testing system of the presentinvention is shown in FIG. 9. The testing systems includes a hand-helddisplay unit 10, a hand-held remote unit 12 and first and second patchcords 14 and 16. Each patch cord comprises a first plug 14A, 16A at oneend, the actual cable 14B, 16B and a second plug 14C, 16C at the otherend. The display unit 10 has a channel link adapter board 18 on which ismounted a first connector jack 20. The jack is exposed to the exteriorof the display unit. Jack 20 can receive the plug 14A or 16A of a patchcord to form a first mated connector pair. When shooting a link, theother plug 14C, 16C of the patch cord mates with a wall jack 22 attachedto the link 24 running inside the walls. The remote unit 14 similarlyhas a channel link adapter board 26 on which is mounted a secondconnector jack 28. Both of the connectors 20 and 28 are preferablyright-angle connectors with appropriate pair-to-pair isolation. An RJ-45jack or a Siemon terra jack for higher frequencies are suitable. Jack 28receives the plug 16A of the second patch cord to form a second matedconnector pair. When shooting a link, plug 16C of the second patch cord16 connects to a wall jack 30 on the end of the link 24. The display andremote units contain appropriate radio frequency and electroniccircuitry for testing the link. The display unit also has user-actuatedswitches for starting and controlling the testing functions, as well asa display that communicates to the user whatever data is appropriate.The display unit also has a computer processor for performing thecalculations described below, and memory to store measured scatteringparameters and other data.

Operation of the LAN testing system is as follows. First a fieldcalibration with the display and remote units and both patch cords mustbe performed. The object of this calibration is to set a measurementreference plane for the display unit and the remote unit by using anytwo patch cords with a set of channel link adapters connected to thedisplay and remote units as shown in FIG. 10. The two patch cords shouldbe made by the same vendor with identical plugs on each end, but they donot have to be the same length.

Scattering Parameters

Since the display and remote units can measure phase, the complete patchcord consisting of the patch cord plugs and the patch cord itself can bemeasured or characterized by measuring their frequency response withscattering, or [S] parameters. From factory calibration, the measurementreference plane on the channel adapter printed circuit board will be atthe input to the right-angle connector jacks 20, 28 on the channel linkadapter boards 18, 26.

Measurement Steps:

1. Connect patch cord 14 between the two units.

2. Measure all four scattering parameters of the first patch cord 14, soconnected, including the mated connector pairs 20,14A and 28,14C at eachchannel link adapter board 18, 26.

3. Save the total, measured scattering data [S_(T)]₁ for the first patchcord 14

4. Connect the second patch cord 1-6 between the two units.

5. Measure all four scattering parameters of the second patch cord 16,so connected, including the mated connector pairs 20,16C and 28,16A ateach channel link printed circuit board 18, 26.

6. Save the total, measured scattering data [S_(T)]₂ for the secondpatch cord 16.

Calculation Steps

1. The elements for the scattering matrix, for each of the patch cords,are a set of simple equations or terms, with known formulation asfollows:

As a 2-port example, consider: ┘:={square root}{square root over (−1)}c:=3.10⁸ M/second

Assume Values for Input Mated LAN Connector Pair A Matrix-[S_(A)]$\begin{matrix}{{SA}_{1,1}:={0.0400 + {0.01 \cdot j}}} & \quad & {{SA}_{1,2}:={0.3 - {0.1 \cdot j}}}\end{matrix}$ $\begin{matrix}{{SA}_{2,1}:={SA}_{1,2}} & \quad & {{SA}_{2,2}:=\overset{\_}{{SA}_{1,1}}} & \quad & {{SA}_{2,2} = {0.04 - {0.01\quad{\mathbb{i}}}}}\end{matrix}$ $\begin{matrix}{{SA}:=\begin{pmatrix}{SA}_{1,1} & {SA}_{1,2} \\{SA}_{2,1} & {SA}_{2,2}\end{pmatrix}} & \quad & {{SA} = \begin{pmatrix}{0.04 + {0.01\quad{\mathbb{i}}}} & {0.3 - {0.1\quad{\mathbb{i}}}} \\{0.3 - {0.1\quad{\mathbb{i}}}} & {0.04 - {0.01\quad{\mathbb{i}}}}\end{pmatrix}}\end{matrix}$ det_A := SA_(1, 1) ⋅ SA_(2, 2) − SA_(1, 2) ⋅ SA_(2, 1)

Patch Cord Matrix-[S_(B)] (Assume that the line is a perfect match)$\begin{matrix}{{L:={2\quad{Meters}}}\quad} & {\quad{{{{Assume}\quad F} = {600\quad{MHz}}},{{NVP} = 0.75}}\quad} & {\alpha:=0.002}\end{matrix}$ $\begin{matrix}{F:={600 \cdot 10^{6}}} & \quad & {{NVP}:=0.75}\end{matrix}$ $\begin{matrix}{{\beta:=\frac{2 \cdot \pi \cdot F}{c \cdot {NVP}}}\quad} & {{\gamma:={\alpha + {\beta \cdot j}}}\quad} & {{\phi:={\gamma \cdot L}}\quad} & {\phi = {{4 \times 10^{- 3}} + {33.51\quad{\mathbb{i}}}}}\end{matrix}$ $\begin{matrix}{{SB}_{11}:=0} & \quad & {{SB}_{12}:={\mathbb{e}}^{- \phi}} & \quad & {{SB}_{21}:={\mathbb{e}}^{- \phi}} & \quad & {{SB}_{22}:=0}\end{matrix}$ $\begin{matrix}{{SB}:=\begin{pmatrix}{SB}_{11} & {SB}_{12} \\{SB}_{21} & {SB}_{22}\end{pmatrix}} & {{SB} = \begin{pmatrix}0 & {{- 0.498} - {0.863\quad{\mathbb{i}}}} \\{{- 0.498} - {0.863\quad{\mathbb{i}}}} & 0\end{pmatrix}}\end{matrix}$ det_B := SB_(1, 1) ⋅ SB_(2, 2) − SB_(1, 2) ⋅ SB_(2, 1)

Output Mated LAN Connector Pair A Matrix-[S_(C)], (Note Relationships to[S_(A)]) $\begin{matrix}{{{SC}_{1,1}:={SA}_{2,2}}\quad} & {{{SC}_{1,2}:={SA}_{2,1}}\quad} & {{{SC}_{2,1}:={SA}_{1,2}}\quad} & {{SC}_{2,2}:={SA}_{1,1}}\end{matrix}$ $\begin{matrix}{{{SC}:=\begin{pmatrix}{SC}_{1,1} & {SC}_{1,2} \\{SC}_{2,1} & {SC}_{2,2}\end{pmatrix}}\quad} & {{SA} = \begin{pmatrix}{0.04 + {0.01\quad{\mathbb{i}}}} & {0.3 - {0.1\quad{\mathbb{i}}}} \\{0.3 - {0.1\quad{\mathbb{i}}}} & {0.04 - {0.01\quad{\mathbb{i}}}}\end{pmatrix}}\end{matrix}$   for  Reference ${SC} = \begin{pmatrix}{0.04 - {0.01\quad{\mathbb{i}}}} & {0.3 - {0.1\quad{\mathbb{i}}}} \\{0.3 - {0.1\quad{\mathbb{i}}}} & {0.04 + {0.01\quad{\mathbb{i}}}}\end{pmatrix}$ det_C := SC_(1, 1) ⋅ SC_(2, 2) − SC_(1, 2) ⋅ SC_(2, 1)

2. To an acceptable degree of accuracy, the patch cord characteristicimpedance Zo is known, and to a very good, first order approximation,may be considered to be Zo=100 Ohms.

3. The electrical length of the patch cord will be known. The length maybe specified by the manufacturer of the tester units, or it can bemeasured by the LAN tester.

4. To an acceptable degree of accuracy, the scattering matrix for themated jack and plug at each end of the patch cord can be assumed to beidentical.

5. Then, using the justifiable assumptions, 1-4 above, and [ST]₁, themeasured total scattering matrix for the first patch cord 14, thescattering matrix for the mated jack and plug pair at each end of thepatch cord can solved for.

6. With the mated connector pair scattering matrix and the scatteringmatrix for patch cord 14, the measurement reference plane may be movedthrough the mated connector pair on the printed circuit board. Thisreference plane location is necessary to perform a channel link test; orthe reference plane may be moved further down the patch cord to within 1or 2 centimeters of the wall jack, in order to perform a permanent linkmeasurement.

7. The same set of measurements and calculations are then made using thesecond patch cord 16.

8. The scattering parameters for the mated connector pairs are saved fortesting throughout the day or until another patch cord set is selected,at which time the field calibration procedure is repeated.

The scattering parameter matrices can be manipulated using linearalgebraic calculations to solve for the elements of the mated LANchannel connector scattering matrix. In this set of calculations, a setof scattering parameters for the mated connector pair is assumed, andfollowing established formulation, the complete, total scattering matrix[S_(T)] is calculated by combining the scattering matrices of the matedconnector pair with that of the patch cord transmission line.

Then, with [S_(T)] as the “given” final, measured result, and with theassumptions for the patch cord transmission line, assumptions 2 and 3above, plus assumption 4 which assumes identical scattering matrices forthe two mated connector pairs, the program solves for the elements ofthe mated connector pair scattering matrix [S_(A)].

The program solves for and calculates the same values for [S_(A)] aswere assumed in the original calculation for the total [S_(T)] matrix.This calculation confirms the mathematical model as correct.

Turning now to a consideration of the phase measurement aspect of theinvention, the LAN tester of the present invention measures therelationship between two signals as it tests LAN cabling for compliancewith published LAN cabling performance standards. The signalrelationships measured by the tester are ratios in magnitude, andinclude the phase relationship between the two signals. Note that thisphase measurement under discussion is the phase between a drive signalvoltage and the corresponding coupled or reflected voltage due to thatsame drive signal. These two signals are measured at a specifiedreference plane determined by factory or field calibration procedures.

Phase difference can be shown between two sinusoidal signals at the samefrequency. In the plot shown in FIG. 11, the V_Drive trace (the solidline) corresponds to the drive signal into the LAN cabling. The V_Meastrace (the dotted line) is the resulting signal to be measured by theLAN tester. Note that the amplitude of V_Meas is 40% of the amplitude ofV_Drive. V_Meas also lags V_Drive by 30 degrees of phase. This laggingphase relationship between V_Drive and V_Meas can also be seen in theplot.

If the ratio of V_Meas to V_Drive is calculated, one then calculates,for example, the crosstalk term relating the drive signal on one LANcable pair and the coupled, crosstalk signal which appears on anotherLAN conductor pair. When the ratio, V_R=V_Meas/V_Drive is calculated,the |V_R|, the magnitude of V_R=|V_R|=|V_Meas|/|V_Drive|=0.4/1.0=0.4.Thus |V_R|=0.4.

The phase between the two signals must be calculated using one of thesignals for the phase reference. In this case, the V_Drive signal isdefined to be the reference signal. The phase relationship of V_Meas isthen said to lag the reference signal, V_Drive, by 30 degrees of phase.Since a phase angle is involved, the ratio, V_R=V_Meas/V_Drive is acomplex number, with a corresponding magnitude, |V_R| and phase angle,φ_(—)=−30 degrees. The negative sign on φ_R indicates that V_Meas lagsV_Drive by 30 degrees in phase. Thus V_R=0.4/_(—)−30 degrees.

Phase may also be calculated from the time relationship of two squarewave signals, by computing the time difference between two correspondingedges of the square wave signals. This is illustrated in FIG. 12 wherethe signals travel from left to right. Note in FIG. 12 the two squarewaves, V_Meas and V_Drive, where the leading edge of V_Meas lags theleading edge of the reference V_Drive square wave by the timedifference, Δt. This time difference may be used to calculate the phasebetween the two signals, by relating Δt to the period, T_(Clock), of aprecise reference clock running at frequency, F_(Clock).T _(Clock)=1/F _(Clock)The phase in degrees, φ_R, between these two square waves, is then:φ_(—) R=360×(Δt/T _(Clock)) degrees

The phase measurement circuit determines the value for Δt, and outputs asignal related to the phase between the two square waves, V_Meas andV_Drive. The LAN tester of the present invention uses a programmablegate array to measure Δt.

The LAN tester can measure phase, which needs to be referenced to ameasurement reference plane, as discussed below.

1. Set the Measurement Reference Plane Initially—During calibration, thephase measurement capability permits the LAN tester to set, or define ameasurement reference plane at one specified point along the LAN link tobe measured. This reference plane, defined during the factorycalibration procedure, may be set anywhere along the link at any point,to permit measurements which are simple and convenient to make. Thecalibration procedure is shown in FIG. 13.

The reference plane location is defined or set during initial factorycalibration at the display and remote ends with the procedure shown inFIG. 13. Plugs containing short-circuit, open-circuit and terminationsare applied in sequence to the jack on the channel link adapter. Sweptfrequency measurements are taken with each plug connected to the jack.From the measured data, which includes phase information, the display orremote end sets its reference plane at the point looking into the jackon the CLA printed circuit board shown with the dotted line. With thisreference plane set at this point, phase information also allows it tobe moved from this point, up and down the patch cord.

2. Move the Measurement Reference Plane—Following patch cord fieldcalibration, phase also allows the LAN tester to easily move thisoriginal calibration reference plane, during link testing. Phase allowsthe original reference plane to be moved to a new reference planelocation at any time during the LAN link testing. Specifically, withphase information, a display end, and/or remote end can each move theirphase reference plane from within the channel link adapter PCB, throughthe mated pair of connectors at the CLA output, anywhere down the lengthof the patch cord and up to the mated pair of connectors at the walljack, in any of the four possible locations as shown in FIG. 9.

2a. Reference plane movement through the mated connector pair from 1 to2, shown in FIG. 14, on the channel link adapter module is performedusing the [S₂₁]_(Connector Pair) data measured and calculated for themated connector pair during patch cord field calibration. This step setsthe reference plane for channel link testing.

2b. Reference plane movement down the patch cord from 2 to 3, shown inFIG. 15, moving down the patch cord is performed using the [S]—parameterdata measured and calculated for the patch cord during fieldcalibration.

Note that the desired length down the patch cord, L_(Line), from 2 to 3is expressed in the physical length units of inches. L_(Line), ininches, needs to be converted into equivalent electrical phase length,φ_(Line) in degrees.

During the patch cord field calibration, the NVP (nominal velocity ofpropagation) for the patch cord is determined through measurement. Fromthis value, the corresponding electrical phase length, φ_(Line), movingfrom 2 to 3 is calculated using:β=(360×f)/(NVP×c) degrees/inch

-   -   where:    -   c=velocity of light in freespace=1.1811×10¹⁰ inches/second    -   f=signal frequency in Hertz        Then φ_(Line) in degrees is calculated using:        φ_(Line) =L _(Line)×(360×f)/(NVP×c) degrees

Relating this formulation to just the patch cord reference planes,moving from 2 to 3 can be seen in FIG. 16.

The measured LAN cable data is moved thru the mated connector pair from1 to 2 using the [S₂₁]_(Connector Pair) data as shown in FIG. 14. Withreference to FIG. 15, which shows how a patch cord length in inches isrelated to the equivalent patch cord electrical length in degrees, FIG.16 relates these terms per the formulation below:$\lbrack S\rbrack_{Patchcord} = \begin{bmatrix}S_{11P} & S_{12P} \\S_{21P} & S_{22P}\end{bmatrix}$

For a reasonably well-matched patchcord, this expression becomes:$\lbrack S\rbrack_{Patchcord} = \begin{bmatrix}0 & {\mathbb{e}}^{{- j}{\quad\quad}\phi\quad{Line}} \\{\mathbb{e}}^{{- j}\quad\phi\quad{Line}} & 0\end{bmatrix}$

If the patch cord has characteristic impedance, Z_(0p), not equal toZ₀=100 Ohms, then the patch cord S_(11p) and S_(22p) are non-zero andare then replaced by non-zero values calculated by using standardtransmission line theory.

Finally, the measured LAN cable data with reference to plane 2, isrelated to plane 3, through the use of, [S]_(Patchcord), the patch cordscattering matrix. $\lbrack S\rbrack_{Patchcord} = \begin{bmatrix}0 & {\mathbb{e}}^{{- j}{\quad\quad}\phi\quad{Line}} \\{\mathbb{e}}^{{- j}\quad\phi\quad{Line}} & 0\end{bmatrix}$From this matrix it can be seen that for a well-matched patch cord, theusual case, there is no effect upon the S₁₁ and S₂₂ mated connector pairterms. The only effect to the mated connector pair scattering matrix isthe added phase term, e^(−jφLine).

Thus, with the patch cord NVP known by measurement or specification, themeasurement reference plane may be moved through the mated connectorpair on the channel link adapter board and down the patch cord aspecified number of inches from plane 2, at the output of the matedconnector pair.

Turning now to a more detailed description of the tester units, theexploded views of FIGS. 17 and 18 show the overall physicalconfiguration of the tester and show how its printed circuit boards arehoused. The tester shown is a display unit 10. It will be understoodthat the remote unit is similar. The tester has a housing including afront enclosure 32 and a rear enclosure 34. The rear enclosure defines areceptacle or well 36 for receiving and mounting a channel link adapterprinted circuit board 37. Inside the housing there is a digital controlmodule 38 that drives and controls an analog stimulus/measurement module40. Both modules are built into printed circuit boards and will bereferred to herein as the digital board and the analog board. The analogboard 40 includes a connector 42 on the underside thereof. Thisconnector is releasably engageable with a mating connector on thechannel link adapter through an opening 43 in the rear enclosure at thebottom of the well 36. A time domain reflectometer (TDR) 44 measurementcapability is provided by a third separate module. Other componentsshown in FIG. 17 include a PCMCIA card holder 46, a universal serial bus(USB) port 48 and a serial port 50. These are mounted on the digitalboard 38. A color display unit 52 and a keyboard 54 are mounted on or inthe front enclosure 32. Further details of the physical arrangement ofthe housing may be as shown and described in U.S. patent applicationSer. No. 09/863,810, filed May 22, 2001 entitled “Apparatus withInterchangeable Modules for Measuring Characteristics of Cables andNetworks”, the disclosure of which is incorporated herein by reference.

The overall function of the digital control module 38 is shown in thedigital control circuit block diagram of FIG. 19. The digital board iscontrolled by a high-speed central processing unit (CPU) 56 driven bythe firmware installed within the tester. Several memory blocks (notshown) may be provided, as well as a RAM memory 58, a small boot flashmemory 60, and a larger boot flash memory 62. The tester communicateswith an external personal computer (PC) 1 either by using the USB 48, orwith a serial interface connection 50 to the CPU 56. Flash memory ornetworking cards 64 can be installed in the tester, which connect to theCPU through the PCMCIA block 46. These cards can be used to storeadditional test results, or to upload new firmware to the CPU. Otherconnections to or from the CPU include the keyboard 54, the colordisplay 52, a speaker phone 66, a real time clock 68 and temperaturesensors 70 to compensate the analog board performance as temperaturerises.

Of utmost importance is communication with the analog board 40 throughthe I/O bus 72. This bus is shown as a separate block because itinterfaces control commands to the analog board 40 from the digitalboard 38, and it returns measured data from the analog board for storagein the display unit memory and for display on the color display 52.

The LAN tester analog circuit block diagram of FIG. 20 shows the majorfunctional blocks on the analog board 40. Other blocks have been omittedfor clarity. The analog board generates a set of continuously varyinglow frequency (LF) and radio frequency (RF) signals which are applied toone selected conductor pair of the LAN cabling through the use of signalswitching relay banks 74 on the analog board. The same relay banks carrythe return signal to be measured from another selected LAN cableconductor pair back into the analog board. Circuit blocks on the analogboard then condition the return test signal and measure itscharacteristics relative to the applied drive signal. The low frequencyLF measurements include cable capacitance, length, conductor wire DCresistance, wire mapping and delay. The circuit blocks associated withthese lower frequency signals are identified by the associated notation.

Note the notation of “MUX’ several places in the block diagram. A MUX isshorthand notation for a multiplexer, which is a switching device thatroutes an input of several different signals to a selected signal path.The LAN tester analog board uses several MUX's since it is afour-channel test instrument, capable of testing two of the possiblefour conductor pairs of the LAN cable under test. The MUX's are requiredfor signal routing and channel to channel signal isolation.

Circuit blocks 76, 78 are shown for RS-485 blocks, one forcommunication, and another for LAN tester interface with the gate arrayand measurement IC 80, and for DC power control and power management onthe analog board.

The analog board 40 also measures the RF parameters of cable crosstalk,return loss and attenuation. Specifically the analog board measures theratio of the amplitude of the returned signal divided by the amplitudeof the RF drive signal. Circuitry has been added to the analog board inthe unit to measure the phase of the returned test signal relative tothe RF drive signal sent out on the selected conductor pair.

The RF drivers 82 send a signal from the RF synthesizer 84 out on onepair of the LAN cable conductors via the RF signal switching relays 74.The drive signal is also sent to the return-loss bridges 86.

The resulting test signal comes into the tester via the same set of RFrelays 74 and is routed through the return-loss bridges 86 to the RFmixer block 88. There it is mixed with the local oscillator (LO) signaland converted into the test IF (intermediate frequency) signal.

As mentioned above, the RF drive signal is also sent into thereturn-loss bridges 86. As shown in FIG. 20, the drive signal sent tothe return-loss bridges enters the mixer 88 and is converted to a phasereference IF signal. All IF signals associated with the LAN measurementare compared with this phase reference IF signal to determine the phaseof that measurement signal.

Once both the Ref IF and Test IF signals have been created they aredelivered to the phase detector 90 and the reference and test magnitudedetector blocks 92 and 94. The phase detector block 90 sends the phaseinformation into the gate array and measurement IC 80. The outputs fromthe reference and test magnitude detectors 92, 94 are sent to theanalog-to-digital (A to D) Mux 96 and then to the A to D converter 98.From there the magnitude ratio signal is sent to the gate array andmeasurement IC (integrated circuit) 80.

The gate array and measurement IC 80 finishes the computation of thephase between the test and reference IF signals, and the ratio of theiramplitudes, to formulate a complex number representation of themeasurement. Output from the IC 80 is placed on the analog I/O bus 72,which communicates with the digital board 38. Thus, the phasemeasurement function for the testing unit is controlled from the digitalboard, but is measured and computed on the analog board. The measurementresults are then carried to the digital board from the analog board.

The LAN tester phase measurement block diagram of FIG. 21 shows thisfunction on a phase measurement system level. This block diagram alsoshows computation of the magnitude ratio on the analog board. The I/Obus 72 carries the control signals from the digital board to the analogboard, and it also carries both the phase and magnitude of the testsignals to the digital board. Once the test signal has been delivered tothe display board it can be stored in the memory or shown in colorgraphic form, plotted on the display screen 52.

Regarding measurement speed, the tester architecture has been designedin such a manner that a LAN cable conductor pair may be driven with RFsignals from either the display or remote test units 10 or 12. All othernon-driven lines may then be simultaneously connected to the measurementcircuitry via the MUX circuitry on the analog boards within each unit.This design feature provides for significantly reduced test times, whilestill providing measurement of test signal magnitude and phase.

In another aspect of the invention, the LAN tester as described abovecould be operated in a so-called dual mode. Briefly, in dual mode theLAN tester will measure once but produce two test results in nominallythe same time as it takes to produce one test result. In other words,the user will press a test button one time and the tester will produceboth channel link test results and permanent link test results. Theseresults could be displayed as selected by the user.

Dual mode measurement for the LAN tester of the present inventionfollows directly from its ability to measure both magnitude and phase,as described above. Looking again at FIG. 9, it will be noted that themeasurement reference plane is set at plane 1 in both the display endunit 10 and the remote end unit 12. This location is set during factorycalibration of the units and it is the starting point for LAN linkmeasurements in the field. This reference plane remains within the unitsand is always used as a starting point for link measurements related tophase.

As set forth above, field calibration determines the properties of thepatch cord cordage 14B, 16B and the properties of the mated pairs 14A/20and 16A/28 of patch cord plugs and CLA jacks. This procedure determinesthe patch cord physical length, its NVP, and the amount of signalattenuation or loss as a signal passes through the length of the patchcord. The display end and remote end patch cords are each characterizedduring field calibration. As indicated, field calibration results areused to determine the properties of the mated plug/jack at the CLA's forboth the display and remote end units in addition to characterizing thesignal properties related to the patch cord cordage vs. frequency.

In dual mode the LAN tester measures the total link in the field. Thetotal link includes everything between reference planes 1 in FIG. 9,namely, the mated plug/jack pairs at each CLA, the patch cord cordage,the mated plug/jack pairs at the walls, and the link running inside thewalls. Then the software de-embeds the mated plug/jack pairs 14A/20 and16A/28 at the display end unit and remote end unit. This can be donesince the characteristics of those plug/jack pairs are known. This ineffect moves the phase measurement reference to planes 2 in FIG. 9,which is at the start of the channel link measurement configuration.De-embedding the plug/jack pairs 14A/20 and 16A/28 provides the channellink measurement. Note that after de-embedding these plug/jack pairsfrom the total link measurement what is left is the channel linkmeasurement.

Once the channel link measurement is defined by the first de-embedding,a second de-embedding step is performed to move the phase measurementreference plane to planes 4 in FIG. 9. The result of the secondde-embedding is the permanent link measurement. Thus, after calibrationonly one link measurement is taken in the field, that for the totallink. From the total link measurement set, the LAN tester can determinethe properties for both channel link and permanent link throughde-embedding techniques, which are made possible by the phasemeasurement circuitry of the present invention.

Since the LAN tester of the present invention has been designed tomeasure phase, the tester uses this capability to measure LAN links in atime efficient manner by treating links as a cascade of linear, two-portnetworks, as shown in FIG. 22.

In FIG. 22 the total link consists of the mated connector pair MP1 atthe display unit 10, the mated connector pair MP4 at the remote unit 12,the patch cord cordage of each patch cord, PC1 and PC2, the matedconnector pairs at each end of the link, MP2 and MP3, and the linkitself. This is what the LAN tester measures in the field. There is aset of four of these cascaded two-ports, one each for Line Pair A, B, C,and D. The LAN tester performs its analysis and operations on all fourof these equivalent cascade models for the total link.

During field calibration, the LAN tester determines the two-port circuitproperties for MP1, PC1, PC2 and MP4 using scattering parameters. Thenwith established de-embedding techniques, the LAN tester resolves thiscascade connection to solve for the properties of the channel andpermanent link from the total link measurement. This resolution isperformed upon Line Pairs A, B, C, and D to solve for the properties ofthe channel and permanent link.

Dual mode offers significant time and cost savings for installers andLAN cable installation vendors since only one link measurement isrequired to determine both channel link and permanent link performance.If a hard-wired PLA and a second, separate CLA were used, two separatemeasurements would be required. Dual mode requires just one measurement.

Preferably, the LAN tester performs its linear two-port circuit analysisusing scattering, or [S] parameters. However, it will be understood thatthis analysis and de-embedding can also be done using other, establishedtwo-port circuit parameters such as [ABCD]-matrix, [Z]-matrix,[Y]-matrix, and [H]-matrix network parameter representations. With phasemeasurement, the LAN tester can also perform its analysis andde-embedding using parameters from any one or a combination of these[ABCD], [Z], [Y], and [H] matrix network parameter representations orother linear two-port network parameter representations.

While a preferred form of the invention has been shown and described, itwill be realized that alterations and modifications may be made theretowithout departing from the scope of the following claims.

1. In a LAN cabling testing system of the type having a display unit anda remote unit and first and second patch cords, the patch cords eachterminating at first and second plugs, and the display and remote unitseach having a jack for receiving a patch cord plug, a plug and jack whenconnected comprising a mated connector pair, the display and remoteunits each having means for sending and receiving a wave form ofselected frequency to and from the other unit through said patch cordsand a LAN link to be tested, an improved method of testing LAN cablingcomprising the steps of: a) calibrating the patch cords and matedconnector pairs, calibration including the step of measuring thescattering parameters of the mated connector pairs and the patch cords;b) connecting the first patch cord to the display unit and one end ofthe link to be tested, and connecting the second patch cord to theremote unit and to the other end of the link to be tested; c) measuringthe total link; d) using the scattering parameters of the matedconnector pairs to move the reference planes at the display unit andremote unit to the necessary locations for performing channel linktesting and storing or displaying the channel link results; and e) usingthe scattering parameters of the mated connector pairs and the patchcords to move the reference planes at the display unit and remote unitto the necessary locations for performing permanent link testing andstoring or displaying the permanent link results.
 2. In a LAN cablingtesting system of the type having a display unit and a remote unit andfirst and second patch cords, the patch cords each having cordageterminating at first and second plugs, and the display and remote unitseach having a jack for receiving a patch cord plug, a plug and jack whenconnected comprising a mated connector pair, the display and remoteunits each having means for sending and receiving a wave form ofselected frequency to and from the other unit through said patch cordsand a LAN link to be tested, an improved method of testing LAN cablingcomprising the steps of: a) measuring the characteristics of the patchcords and mated connector pairs; b) connecting the first patch cord tothe display unit and one end of the link to be tested, and connectingthe second patch cord to the remote unit and to the other end of thelink to be tested; c) measuring the characteristics of the total link;d) calculating channel link measurements by de-embedding from the totallink measurements the characteristics of the mated connector pairs; ande) calculating permanent link measurements by de-embedding from thechannel link calculation the characteristics of the patch cord cordage.3. The method of claim 2 further comprising the step of storing thechannel link calculation.
 4. The method of claim 2 further comprisingthe step of storing the permanent link calculation.
 5. The method ofclaim 2 further comprising the step of comparing the channel linkcalculation with a selected industry standard and displaying a pass orfail indication based on said comparison.
 6. The method of claim 2further comprising the step of comparing the permanent link calculationwith a selected industry standard and displaying a pass or failindication based on said comparison.
 7. A LAN cabling testing system,comprising: first and second patch cords each including cordage andterminating at first and second plugs; a hand-held display unit and ahand-held remote unit, each one of said units including means forsending and receiving a wave form of selected frequency to and from theother of said units through said patch cords and a LAN link to betested; the hand-held display unit including a jack for receiving a plugof one of the patch cords, said jack and plug defining a first matedconnector pair; the hand-held remote unit including a jack for receivinga plug of the other of the patch cords, said jack and plug defining asecond mated connector pair; phase measuring means for measuring phasein one of the display or remote units; and wherein one of the displayunit and remote unit further comprises electronic storage means forstoring the characteristics of the mated connector pairs, andcalculating means programmed to de-embed the connector pairscharacteristics from a total link measurement to calculate the channellink measurements.
 8. The LAN tester of claim 7 wherein the electronicstorage means further stores the characteristics of the cordage of thepatch cords and the calculating means is programmed to de-embed thecordage characteristics from the calculated channel link measurement tocalculate the permanent link measurements.
 9. A LAN cabling testingsystem, comprising: first and second patch cords each terminating atfirst and second plugs; a hand-held display unit and a hand-held remoteunit, each one of said units including means for sending and receiving awave form of selected frequency to and from the other of said unitsthrough said patch cords and a LAN link to be tested; the hand-helddisplay unit including a jack for receiving a plug of one of the patchcords, said jack and plug defining a first mated connector pair; thehand-held remote unit including a jack for receiving a plug of the otherof the patch cords, said jack and plug defining a second mated connectorpair; phase measuring means for measuring phase in one of the display orremote units; and wherein one of the display unit and remote unitfurther comprises electronic storage means for storing the two-portperformance representation of the patch cords and the mated connectorpairs, and calculating means programmed to use the stored two-portperformance representation to move the phase reference planes to thenecessary locations for performing channel link or permanent linktesting.
 10. In a LAN cabling testing system of the type having adisplay unit and a remote unit and first and second patch cords, thepatch cords each terminating at first and second plugs, and the displayand remote units each having a jack for receiving a patch cord plug, aplug and jack when connected comprising a mated connector pair, thedisplay and remote units each having means for sending and receiving awave form of selected frequency to and from the other unit through saidpatch cords and a LAN link to be tested, an improved method of testingLAN cabling comprising the steps of: a) calibrating the patch cords andmated connector pairs, calibration including the step of measuring thetwo-port performance representation of the mated connector pairs and thepatch cords; b) connecting the first patch cord to the display unit andone end of the link to be tested, and connecting the second patch cordto the remote unit and to the other end of the link to be tested andshooting the link to be tested; and c) using the two-port performancerepresentation of the mated connector pairs and the patch cords to movethe reference planes at the display unit and remote unit to thenecessary locations for performing channel link or permanent linktesting.
 11. A LAN cabling testing system, comprising first and secondpatch cords each terminating at first and second plugs, a hand-helddisplay unit and a hand-held remote unit each including a channel linkadapter card having a jack suitable for receiving a plug of a patchcord, each one of said units including means for sending and receiving awave form of selected frequency to and from the other of said unitsthrough said patch cords and a LAN link to be tested, at least one ofthe display unit and remote unit including phase measuring means formeasuring phase in one of the display or remote units, said one of thedisplay or remote units further comprising an electronic storage meansfor storing a two-port performance representation of the patch cords andmated plug and jack pairs, and calculating means programmed to use thestored two-port performance representation to move the phase referenceplanes along the patch cords such that channel link and permanent linktests can be made using the channel link adapter card.
 12. In a LANcabling testing system of the type having a display unit and a remoteunit and first and second patch cords, the patch cords each terminatingat first and second plugs, and the display and remote units each havinga jack for receiving a patch cord plug, a plug and jack when connectedcomprising a mated connector pair, the display and remote units eachhaving means for sending and receiving a wave form of selected frequencyto and from the other unit through said patch cords and a LAN link to betested, an improved method of testing LAN cabling comprising the stepsof: a) calibrating the patch cords and mated connector pairs,calibration including the step of measuring the two-port performancerepresentation of the mated connector pairs and the patch cords; b)connecting the first patch cord to the display unit and one end of thelink to be tested, and connecting the second patch cord to the remoteunit and to the other end of the link to be tested; c) measuring thetwo-port performance representation for the total link; and d)de-embedding the two-port performance representations of the matedconnector pairs from the total link measurement to calculate the channellink characteristics.
 13. The method of claim 12 further comprising thestep of de-embedding the two-port performance representations of thepatch cords from the channel link characteristics to calculate thepermanent link characteristics.
 14. The method of claim 13 wherein thesteps of measuring the two-port performance representations are furthercharacterized by using two-port circuit parameters selected from thegroup of [S], [ABCD], [Z], [Y], and [H]-matrix network parameters. 15.The method of claim 12 wherein the steps of measuring the two-portperformance representations are further characterized by using two-portcircuit parameters selected from the group of [S], [ABCD], [Z], [Y], and[H]-matrix network parameters.